The human jaw, or mandible, performs a wide array of motions beyond simple opening and closing. These intricate movements are essential for daily activities like speaking, chewing, and swallowing. Among these complex actions lies a specific, often overlooked, movement known as the Bennett movement. Understanding this jaw motion provides insight into the sophisticated mechanics governing oral function.
Basic Jaw Mechanics
The human jaw connects to the skull through two temporomandibular joints (TMJs), located just in front of each ear. These joints act as hinges, allowing the jaw to move up and down, forward (protrusion), and backward (retrusion). Along with these primary motions, the TMJs also facilitate side-to-side movements.
This side-to-side motion is termed lateral excursion, important for grinding food during chewing. During lateral excursion, the mandible shifts to one side. The coordinated action of various muscles, including the masseter, temporalis, and pterygoid muscles, enables these mandibular movements.
The Bennett Movement Unveiled
The Bennett movement refers to the bodily side-shift of the mandible during a lateral jaw movement. This lateral displacement happens towards the “working side.” It is a translation of the entire mandible, rather than just a rotation.
This movement is not a single, continuous shift but comprises two components: immediate side shift and progressive side shift. The immediate side shift occurs at the very beginning of the lateral movement, where the non-working side condyle moves straight medially. The progressive side shift then accompanies the continued lateral movement, with a gradual translation of the condyle. This bodily shift, typically ranging from 1 to 4 mm, is influenced by the anatomy of the temporomandibular joint and its surrounding ligaments.
Its Role in Oral Health
The Bennett movement is important for normal oral function, particularly in chewing, known as mastication. This side-shift allows the upper and lower teeth to interact effectively, enabling proper shearing and grinding of food. Without this specific lateral motion, food breakdown would be compromised.
The Bennett movement contributes to the interaction between opposing teeth during lateral excursions. It helps guide the teeth along their paths, preventing excessive or uneven wear on tooth surfaces. The movement also aids in speech articulation and jaw comfort, facilitating smooth jaw dynamics.
When Movement Varies
Variations in the Bennett movement can occur naturally, but sometimes they may indicate or contribute to oral health concerns. For instance, an atypical Bennett movement can be associated with temporomandibular joint (TMJ) disorders, which involve pain and dysfunction in the jaw joints and surrounding muscles. Such variations might also lead to uneven tooth wear over time, as teeth may not glide against each other as intended.
Dentists consider the characteristics of the Bennett movement during diagnosis and treatment planning for dental procedures. This is particularly relevant when creating dental restorations like crowns or dentures, as understanding the patient’s unique jaw movements helps ensure proper bite alignment and long-term stability. Recognizing these subtle shifts is part of providing comprehensive care for jaw function.